1. Field of Invention
The present invention relates to a working vehicle, and more particularly to a layout structure of a hydraulic continuously variable transmission apparatus with respect to a transmission case, in a hydromechanical continuously variable transmission apparatus of the working vehicle.
2. Background Art
Conventionally, a working vehicle such as a tractor, a carrier vehicle or the like is structured such that rear wheels are driven by arranging an engine in a front portion of a vehicle body and arranging a transmission case in a rear portion, and is provided with a transmission constituted by a transmission mechanism, a clutch mechanism and the like for inputting a power of the engine and transmitting the power to an axle after changing gear. In a transmission structure of the working vehicle, there are proposed a lot of structures provided with a main transmission mechanism using a hydrostatic continuously variable transmission apparatus (a hydrostatic transmission, hereinafter refer to “HST” for short). Further, particularly in recent years, there is widely produced a hydromechanical continuously variable transmission apparatus (a hydromechanical transmission, hereinafter refer to “HMT” for short) structured by combining the HST and a differential mechanism, because it has excellent operability at a time of shifting gears in comparison with the mechanical transmission mechanism and has excellent energy efficiency in comparison with the HST.
In this case, as a layout of a traveling drive system of the working vehicle employing the HST mentioned above, there is proposed a structure in which a hydraulic pump and a hydraulic motor constituting the HST are separately arranged, and are hydraulically connected, and an engine power is output to the hydraulic motor, however, the structure is generally made such that the engine power is transmitted to the transmission (HST) via a transmission shaft corresponding to an output shaft of the engine.
Specifically, there are proposed a monocoque body structure in which a transmission case is directly connected to an engine so as to double as a machine body frame, and a structure in which an engine and a transmission case are separately arranged and an output shaft of the engine is inserted into the transmission case. For example, patent document 1 discloses a working vehicle provided with an input split type HMT, and patent document 2 discloses a working vehicle provided with an output split type HMT, in each of which a monocoque body structure is formed by directly connecting an engine and a transmission case (refer to patent document 1 and patent document 2). Further, patent document 3 discloses a working vehicle in which an HST is attached to an outer side of a transmission case, and an output shaft from an engine is inserted as an input shaft of the HST to the HST (refer to patent document 3).
Patent Document 1: Japanese Unexamined Patent Publication No. 2000-18367
Patent Document 2: Japanese Unexamined Patent Publication No. 2002-139126
Patent Document 3: Japanese Unexamined Patent Publication No. 1996-104149
However, in the conventional layout of the traveling drive system of the working vehicle, the following problems are generated.
As disclosed in the patent document 1 and the patent document 2, in the structure in which the HST is inward provided in the transmission case so as to be arranged as a part of the machine body frame, there is a case that a working fluid supplied to and discharged from the HST (the hydraulic pump and the hydraulic motor) and a working fluid supplied to and discharged from the other elements such as the clutch and the like are mixed within the transmission case. Particularly in the HMT, since the differential mechanism is attached simultaneously with the HST at a time of assembling the transmission, a dust is generated, and there is a case that the dust gets into the transmission case. Accordingly, a foreign material such as the dust or the like is mixed into the hydraulic pump and the hydraulic motor of the HST, and a malfunction tends to be generated in a cylinder, a piston or the like of the hydraulic pump and the hydraulic motor.
Further, as disclosed in the patent document 1 to the patent document 3 mentioned above, in the structure in which the output shaft of the engine serving as the transmission shaft passes through the HST (the hydraulic pump and the hydraulic motor) in a longitudinal direction, the output shaft mentioned above forms an obstacle. It is hard to attach and detach the HST to and from the transmission, and it is troublesome to assemble and disassemble the transmission for maintenance.
The problem to be solved by the invention exists in changing a layout structure of an HST (a hydraulic pump and a hydraulic motor) constituting a continuously variable transmission apparatus in a working vehicle so as to achieve a simplification of the structures of the working vehicle and a transmission, thereby increasing the ease of a maintenance.